There are two options. First, you can get a 4x5 camera and the Polaroid 405 or Fuji PA-145 back. Both of these take the 3.25"x4.25" film and use the full frame. The backs are hard to find, and when you find one, expect to pay $100-$200 for it.

Your other option is to buy a converted Polaroid 110A. It's not a 4x5, but it is a folder, and will give you full frame on 3.25"x4.25". If you don't need/want to swap lenses, this is an easy way to get good quality and full frame: